SGI 2010 Field Trip Guidebook The Corchia Cave (Alpi Apuane): a 2 Ma long temporal window on the Earth climate Edited by Giovanni Zanchetta Dipartimento di Scienze della Terra, University of Pisa, Italy Ilaria Isola Istituto Nazionale di Geofisica e Vulcanologia, sezione di Pisa, Italy Leonardo Piccini Dipartimento di Scienze della Terra, University of Florence, Italy Andrea Dini Istituto di Geoscienze e Georisorse, CNR Pisa, Italy With contributions of Ilaria Baneschi, Massimo Guidi Istituto di Geoscienze e Georisorse CNR Pisa, Italy Russell Drysdale Department of Resource Management and Geography, University of Melbourne, Australia Giancarlo Molli, Flavio Milazzo, Diego Pieruccioni, Eleonora Regattieri Dipartimento di Scienze della Terra, University of Pisa, Italy SGI 2010 Field Trip Guidebook Index 1. Introduction 4 2. General geomorphological and geological framework of Alpi Apuane 8 Karst geomorphology 9 Geology of the Alpi Apuane 12 Ore deposits: history and metallogeny 14 3.The Mount Corchia 19 Geological setting 19 The Levigliani Hg deposit 21 The karst system 28 General hydrology 32 The monitoring system, hypogean climate and water geochemistry 33 Hypogean climate 33 Water geochemistry 36 Drips 37 Stable isotope water geochemistry 38 Paleoclimatology 40 Paleoclimate studies on Alpi Apuane caves with special reference on Corchia 44 The laghetto core: ca 1,000000 continuous record of climatic changes 46 The last interglacial (MIS5e) and its end 49 The Holocene hydrological changes and Sapropel S1 deposition 51 Field stops 53 Corchia Cave 53 1. Corchia Tourist entrance 53 2. Galleria Franosa 54 3. Galleria degli Inglesi 55 4 Galleria del Venerdì 55 2 SGI 2010 Field Trip Guidebook 5. The Galleria delle Stalattiti 56 The Levigliani mercury mine 57 6. Cava Romana 57 7. Cavetta Tunnel 60 8 .Speranza 61 4. References 63 3 SGI 2010 Field Trip Guidebook 1. INTRODUCTION Monte Corchia (Northern Tuscany, Italy, Fig. 1.1) is one of the most emblematic geological structure of the Alpi Apuane but this is not the only peculiar aspect of this territory. Within a very small area it is possible to combine geology, mineralogy, geomorphology and paleoclimatology with a warm and friendly welcome from the typical Apuan village of Levigliani. Within the Mesozoic carbonate succession (marble and dolostone) of the Corchia synclinal core, the longest Italian cave develops with 52 km of pits and galleries (Fig. 1.2). Discovered the 11 October 1840 by Emilio Simi, a local naturalist, the Monte Corchia cave system has long been one of the most famous caves of Italy. Initial surveying of the cave dates to the second half of the 19th century, but systematic explorations began only during the first half of the 20th century. In 1934, speleologists from Florence attained the depth of about 540 m below the entrance, the greatest depth ever reach in the world at that time. In the second half of the last century the Monte Corchia system attracted hundreds of speleologists from Italy and abroad. In the 1980s the collaboration, and some time the competition, among several Italian caving groups allowed the exploration of more than 50 km of cave passages with the depth reaching 1185 m. Being part of the vast district of the Alpi Apuane, The Monte Corchia massif is a site of historical and modern marble exploitation, which represents one of the most traditional sources of local income. In the recent past (1985), the area of Monte 4 SGI 2010 Field Trip Guidebook Corchia has been included in the Alpi Apuane Regional Park and in the 2001 part of the cave system was opened to the public. Figure 1.1 - Sketch geological map of Alpi Apuane. The distribution of ore deposits inside the metamorphic units is also shown. 5 SGI 2010 Field Trip Guidebook The opening of the tourist cave has shown that local economic benefits can arise from a more correct use of the landscape and by the additional incoming produced by tourism. A local cooperative (Cooperativa Sviluppo e Futuro Levigliani) has, in last years, promoted important activity in the area for attracting tourism joining the different peculiarities of this land. The Federazione Speleologica Toscana (Tuscan Speleological Federation) understood the new scientific potential of the cave, and has logistically and economically supported (since the 1998) researchers of the University of Pisa, INGV and CNR for using speleothems (cave concretions including stalagmites and stalactites) as an archive for reconstructing past climate conditions. So, in recent years, the Monte Corchia Cave system has turned out to be one of the most promising archives for reconstructing the paleoclimate and paleoenvironment in the Mediterranean basin (Drysdale et al. 2004, 2005, 2007, 2009; Zanchetta et al. 2007), with implications for the chronology of climatic events at the global scale (Drysdale et al. 2007, 2009). Owing to this new field of research, the Monte Corchia karst is not anymore seen as a locality where different aspects of local geology and geomorphology can be observed, but it is now studied as an unique system in which the geological structure conditioned the development of the cave and the history of deformation and mineralization have influenced the chemistry of drip waters from which speleothems precipitate. Moreover, the radiometric measurement of the concretions gives unique information on the timing of cave passages formation and then the recent uplift history of this sector of the Apennine. This field 6 SGI 2010 Field Trip Guidebook trip is an update synthesis of the work conducted by specialists who are currently working on this cave system from several points of view, which are producing a new and fresh holistic view of this environment. 7 SGI 2010 Field Trip Guidebook 2. GENERAL GEOMORPHOLOGICAL AND GEOLOGICAL FRAMEWORK OF THE ALPI APUANE Monte Corchia is located in the south-western part of the Alpi Apuane, a mainly calcareous mountain range, about 50 km long, 20 km wide and up to 1947 m high, in the NW of Tuscany (Fig. 1.1). The alpine-like landscape of this region is due to several factors, among which the complex structural setting play a relevant role. In particular, the very steep beddings and the tectonic repetition of different rocks (mainly limestone and phyllite) have enhanced the role of differential erosion processes. The present topography is presumed to be the result of heavy fluvial erosion accompanied by rapid tectonic uplift during Early Pleistocene (Piccini et al., 2003b; Bartolini, 2003, Fellin et al., 2007). Glacial and periglacial processes reshaped the landscape during the last glacial stages, emphasising the “alpine-like” features of the Alpi Apuane (Braschi et al., 1986). In this respect it is interesting to remember that the first Quaternary glacial remain of the whole Apennine was discovered in the Alpi Apuane (Cocchi,1872; Stoppani, 1872). The Apuan glacial remains have very interesting characteristics: in fact, in the Apuan chain there are the lowest glacial deposits of the whole Italian peninsula. In their most extensive phase of development the Equilibrium Line Altitude of the glaciers has been calculated for the internal areas at ca. 1200-1300 asl (Braschi et al., 1986); this is the lowest recorded in the Apennine chain. Several studies (e.g. see Federici, 2005 for a recent review) have reported the 8 SGI 2010 Field Trip Guidebook presence of at least 9 valley glaciers on the northern side of the Alpi Apuane with the estimated fronts located in an extraordinarily low position (down to 600 m asl). Monte Corchia forms part of the main surface drainage divide of the Alpi Apuane, and it is located between the coastline of Mar Ligure and the inner basin of the Serchio River. For this reason, local climate is characterized by strong spatial variations as a function of elevation and distance from the sea. This mountain ridge is one of the rainiest parts in Europe. Mean annual rainfall exceeds 2500 mm over a large part of the chain and on the central ridges it is more than 3000 mm/yr (Rapetti and Vittorini, 1994; Piccini et al., 1999). Campagrina station, very close to Monte Corchia, has a mean annual precipitation of 3055 mm, one of the highest values in Italy. Karst geomorphology Surface karst landforms are not well developed in the Apuane because the high relief and regional climatic conditions (i.e. high temperature excursions and rainfall up to 3500 mm/yr) enhance mechanical-denudation processes. In particular, mechanical erosion must have been very active during the last glacial and postglacial phases, destroying most of the previous surface karst landforms. Only in some restricted low-relief areas are small to medium-scale karst landforms. On the contrary, karst caves represent one of the most important morphological features of the Alpi Apuane: nine caves are deeper than 1000 m and 21 caves are longer than 3000 m. Most of the caves are percolation-vadose 9 SGI 2010 Field Trip Guidebook in origin with a predominance of vertical development. The deepest caves reach local piezometric surfaces at elevations between 350 and 550 m asl. Based on the vertical distribution of the phreatic and epiphreatic passages in the caves, three major generations of base-level caves can be identified (Piccini, 1997). In the largest cave system, the Monte Corchia Complex (Fig. 1.2), at least four levels are preserved, each cut vertically by a succession of percolation (vadose) caves (Piccini, 1997). In the central part of the massif, the uppermost level is preserved at an altitude of 1600-1700 m asl, whilst the second and most widely developed generation occurs between 1000 m to 750 m asl. In the Corchia Complex, the situation is slightly different, with the first generation lying above 1450 m asl, and the second at between 1000 and 1200 m asl. The latter form a wide anastomosing network that was subsequently affected by a major phase of vadose entrenchment.